Manufacture of superconducting wire



United States Patent Olfice 3,378,916 MANUFACTURE OF SUPERCONDUCTINGWIRE Peter Robinson, Fossway, Newcastle-upon-Tyne, England, assignor toInternational Research & Development Company Limited, Fossway,Newcastle-upon-Tyne, England No Drawing. Filed Oct. 21, 1965, Ser. No.500,218 Claims priority, application Great Britain, Oct. 30, 1964,44,416/64 2 Claims. (Cl. 29-599) The present invention relates toprocesses for the production of superconducting niobium-zirconium alloywire.

Niobium-zirconium alloys, in the form in which they are normallyobtained, are relatively brittle and dilficult to fabricate into wire.This is particularly true of alloys with high oxygen, carbon, hydrogenand nitrogen contents.

The present invention provides a process in which the material issubjected to a series of treatments to overcome these difiiculties andto produce niobium-zirconium alloy wire of improved superconductingproperties.

It is necessary to start with a material having a refined crystalstructure, that is to say, a material in which dendritic crystalstructure and high concentrations of impurities are substantiallyabsent. When the material has been formed by casting, the as-caststructure should be broken down by mechanical working, prelfierably ho-tworking. When the material has been formed by powder metallurgytechniques, the amount of working necessary to produce a refined crystalstructure may be considerably less.

The process in accordance with the invention for the production ofsuperconducting niobium-zirconium alloy wire comprises the followingsteps:

('1) Heat-treating a niobium-zirconium material having a refined crystalstructure as herein defined, in a temperature range l000-l250 C. underinert conditions for 3 -120 minutes.

(2) Quenching the material as quickly as possible to retain the secondphase constituents in solution.

(3) Working the material at a temperature below 500 C. to reduce itscross-section and removing any surface defects which may be present.

(4) Further heat-treating the material at a temperature in the range 750C.825 C. under inert conditions for 15430 minutes.

(5) Enclosing the material in a sheath of different material havingsubstantially similar working properties to the material regardingductility, rate of work-hardening and hardness.

(6) Deforming the material and sheath together to the required finalcross-section of the material.

(7) Dissolving the sheath.

(8) Copper-plating the material.

-T he material of the sheath may be Inconel alloy. The copper-platingstep preferably includes hydriding the material and depositing a film ofnickel before the copper is deposited.

The process will now be described in more detail with the aid of anexample. A cast ingot of niobium-zirconium was used having the analysisby weight: Zirconium V 27.8%, balance niobium, oxygen 74 parts permillion, ni-

trogen 50 parts per million, carbon 125 parts per million and hydrogen 2par-ts per million. The ingot was hotextruded to a diameter of to breakdown the as-cast structure and then heat-treated at 1200 C. for one hourin an atmosphere of static inert gas, for example, argon, or in vacuum.The heat treatment was carried out in a metal canister, for example, ofmild steel protected against oxidation by a refractory frit and thewhole subsequently quenched in water at room temperature (about C).

3,378,916 Patented Apr. 23, 1968 The heat-treated ingot was then coldswaged at room temperature to 0.110 inch diameter rod and dressed, forexample, "by grinding and filing, to remove any surface defects. It wasthen given further heat treatment at 800 C. for fifteen minutes in astatic argon atmosphere. This treatment was carried out in anargon-filled copper tube which was a loose fit on the rod. The ends ofthe tube were sealed by high-temperature brazing. The canned rod waspassed continuously through a furnace to give the desired heattreatment.

After removal from the copper can the rod was placed in a cold drawnInconel tube 0.160 outer diameter and 0.130 inner diameter. One end ofthe tube was swaged on to the rod and the tube then drawn tightly on tothe rod. The composite member was then cold drawn until the diameter ofthe wire forming the core of the composite member was 0.010 inch.

The In conel sheath was then dissolved off the rod by an electrolyticprocess by a batch technique using a solution of 5% sulphuric acid at2.3 volts potential difference.

Finally, the wire was plated using a continuous process apparatus suchas is described in our oopending application No. 27,614/64. The wire wasfirst degreased then etched in 10% hydrofluoric acid solution at 38 C.and then hydrided electrolytically in 2% hydrofluoric acid (cold) at acurrent density of 40 amps. per square foot.

A nickel flash plating 0.0001 inch thick was then given to the wire at acurrent density of 40 amps. per square foot and finally copper wasdeposited from an acid sulphate bath at a current density of amps. persquare foot to give a final overall plating thickness on the wire of0.001 inch.

In the casting of the niobium-zirconium alloy the second phaseconstituents, that is to say, oxygen, carbon, hydrogen and nitrogen, arepreferentially precipitated at the grain boundaries, resulting inenrbrittlement of the material. After extrusion of the ingot to breakdown the as cast structure, the first heat treatment produces solutionof the second phase constituents and the quenching retains most of thesecond phase constituents in solution. Any second phase constituentswhich are precipitated during the quenching are dispersed throughout thematerial and are thus less harmful. The resulting reduction inembrittlement means that alloys with high oxygen, carbon, hydrogen andnitrogen contents can be fabricated. The case of fabrication can beestimated by measuring the hardness of the material before and after theinitial heat treatment. It is found that the all-0y can be more easilyfabricated if its hardness before the heat treatment is below 26-5 VPN(Vickers Pyramid Number) and is not increased by the treatment.

The initial heat treatment followed by cold working and subsequentthermal precipitation treatment (Step 4) has a beneficial effect on thesuperconducting properties of the material.

The process can be used to advantage from the points of view offabrication and improvement of superconducting properties with mostniobium-zirconium alloys.

In the example described above the working of the material after thefirst heat treatment took place at room temperature, but this workingcan be carried out at temperatures up to about 500 C.

Materials other than Inconel can be used for the enclosing sheathproviding they have properties similar to those of the niobium-zirconiumalloy regarding ductibility, rate of work-hardening and hardness. Thepurpose of the sheath is to reduce the effect of ga-lling between thewire and the die through which the wire is drawn.

I claim:

1. A method or process for the production of super- 3 conductingniobium-zirconium alloy wire comprising the following steps:

(a) heat-treating a niobium-zirconium material containing a second phaseconstituent and having a substantially non-dendritic refined crystalstructure sub- 'stantially free of high concentrations of impurities, ina temperature range 10001250 C. under inert conditions for 30-120minutes, whereby said second phase is placed in solution with saidmaterial;

(b) quenching the material as quickly as possible to retain thesecond-phase constituents in solution;

(c) Working the material at a temperature below 500 C. to reduce itscross section and removing any sur- =fa'ce defects which may be present;

(-d) further heat-treating the material at a temperature in the range750 C.8"25 C. under inert conditions for 15-130 minutes;

(e) enclosing the material in a sheath of different material havingsubstantially similar working properties to the material regardingductility, rate of workharden-ing and hardness;

(f) deforming the material and sheath together to the required finalcross-section of the material; (g) dissolving the sheath; '(h)copper-plating the material. 2. A process as claimed in claim 1 in whichthe copperplating step includes hydriding the material and depositing afilm of nickel before the copper is deposited.

References Cited UNITED STATES PATENTS 3,109,963 1 1/1963 Geballe 295993,131,469 5/ 1964 Glaze. 3,204,326 9/1965 Granitas. 3,218,693 111/1965Allen et al. 29-599 3,239,919 '3/ 19661 Levi. 3,277,564 IO/1966 Webberet a1. 29419 JOHN F. CAMPBELL, Primary Examiner.

20 PAUL M. COHEN, Assistant Examiner.

1. A METHOD OR PROCESS FOR THE PRODUCTION OF SUPERCONDUCTINGNIOBIUM-ZIRCONIUM ALLOY WIRE COMPRISING THE FOLLOWING STEPS: (A)HEAT-TREATING A NIOBIUM-ZIRCONIUM MATERIAL CONTAINING A SECOND PAHSECONSTITUENT AND HAVING A SUBSTANTIALLY NON-DENDRITIC REFINED CRYSTALSTRUCTURE SUBSTANTIALLY FREE OF HIGH CONCETRATIONS OF IMPURITIES, IN ATEMPERATURE RANGE 1000*-1250*C. UNDER INERT CONDITIONS FOR 30-120MINUTERS, WHEREBY SAID SECOND PHASE IS PLACED IN SOLUTION WITH SAIDMATERIAL; (B) QUENCHING THE MATERIAL AS QUICKLY AS POSSIBLE TO RETAINTHE SECOND-PHASE CONSTITUENTS IN SOLUTION; (C) WORKING THE MATERIAL AT ATEMPERATURE BELOW 500* C. TO REDUCE ITS CROSS SECTION AND REMOVING ANYSURFACE DEFECTS WHICH MAY BE PRESENT; (D) FURTHER HEAT-TRETING THEMATERIAL AT A TEMPERATURE IN THE RANGE 750*C.-825-C. UNDER INERTCONDITIONS FOR 15-130 MINUTES; (E) ENCLOSING THE MATERIAL IN A SHEATH OFDIFFERENT MATERIAL HAVING SUBSTANTIALLY SIMILAR WORKING PROPERTIES TOTHE MATERIAL REGARDING DUCTILITY, RATE OF WORKHARDENING AND HARDNESS:(F) DEFORMING THE MATERIAL AND SHEATH TOGETHER TO THE REQUIRED FINALCROSS-SECTION OF THE MATERIAL; (G) DISSOLVING THE SHEATH; (H)COPPER-PLATING THE MATERIAL.